Tests: Fix CPackComponents NSIS install root

Without `CPACK_VERBATIM_VARIABLES` a path with backslashes does not make
it through `CPackConfig.cmake` properly.  Just use forward slashes which
NSIS seems to understand anyway.

Tests/CPackComponents/CMakeLists.txt

@@ -79,7 +79,7 @@ set(CPACK_NSIS_MENU_LINKS
   )
 
 # Suggested default root for end users of the installer:
-set(CPACK_NSIS_INSTALL_ROOT "C:\\Program Files\\CMake Tests Install Root")
+set(CPACK_NSIS_INSTALL_ROOT "C:/Program Files/CMake Tests Install Root")
 
 # Include CPack to introduce the appropriate targets
 include(CPack)